| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 0.6 | 163 |
| 2014 | 0.4 | 168 |
| 2013 | 0.7 | 154 |
| 2012 | 0.3 | 175 |
| 2011 | 0.4 | 169 |
| 2010 | 0.6 | 166 |
| 2009 | 1 | 147 |
| 2008 | 1.3 | 152 |
| 2007 | 1.6 | 144 |
| 2006 | 0.9 | 153 |
| 2005 | 0.7 | 144 |
| 2004 | 0.7 | 143 |
| 2003 | 0.9 | 124 |
| 2002 | 0.5 | 129 |
| 2001 | 0.6 | 125 |
| 2000 | 0.4 | 133 |
| 1999 | 0.4 | 132 |
| 1998 | 0.5 | 128 |
| 1997 | 0.3 | 133 |
| 1996 | 0.2 | 136 |
| 1995 | 0.2 | 124 |
| 1994 | 0.2 | 115 |
| 1993 | 0.2 | 110 |
| 1992 | 0.2 | 91 |
| 1991 | 0.2 | 95 |
| 1990 | 0.1 | 100 |
| 1989 | 0.1 | 93 |
| 1988 | 0.1 | 83 |
| 1987 | 0.1 | 81 |
| 1986 | 0 | 94 |